Simple / Compound Interest Calculator

Supports Simple Interest and Compound Interest

Interest Calculator

Enter your interest parameters to calculate returns

How to Use the Interest Calculator

👉 Step-by-step guide

Enter the principal amount you want to invest or loan (the main money amount). Use the Amount field - decimals are allowed.

Enter the annual interest rate (%) in the Rate of Interest field. For example, enter 7.5 for 7.5% per year.

Set the tenure in the Time field and choose Years or Months from the dropdown. The calculator will convert values correctly for simple and compound calculations.

Select Simple Interest for linear interest calculation or Compound Interest to compound returns. For compound interest, pick the compounding frequency (monthly, quarterly, etc.).

Click "Calculate Interest" to compute the interest and total amount. Results appear below with a per-period breakdown when available. Review Principal, Interest and Total Amount.

Use the Reset button to clear inputs and try different scenarios. Tip: tweak rate, time or frequency to compare outcomes quickly.

About Interest Calculator

This Interest Calculator helps you quickly estimate returns on investments or interest owed on loans using either Simple Interest or Compound Interest methods. It converts inputs (amount, annual rate, time) correctly for both years and months and supports multiple compounding frequencies (annual, semi-annual, quarterly, monthly, daily).

How the calculations work

Simple Interest: Interest = P × r × t, Total = P + Interest (where r is annual rate in decimal and t is time in years).
Compound Interest: A = P × (1 + r/n)^(n×t) where n is compounding periods per year and A is the maturity amount.

Notes & behavior
  • When you select Months the calculator converts months to years (months ÷ 12) before using formulas.
  • For compound interest the per-period interest and breakdown table show how the balance grows each compounding period.
  • Inputs accept decimals and the result is rounded for display; underlying calculations use full precision for accuracy.
  • This tool provides estimates for planning and comparison - it is not a substitute for bank statements, tax advice, or financial consultation.
Tips

Try different frequencies and tenures to see how compounding frequency impacts long-term returns - small rate or frequency changes can meaningfully affect outcomes.

What Makes Our Interest Calculator Unique?

  • Per-period breakdown: Detailed table showing balance and interest for each compounding period.
  • Years & months support: Enter time in years or months - calculator auto-converts for accurate results.
  • High precision: Uses full precision for calculations and rounds only for display to avoid drift.
  • Multiple frequencies: Choose annual, semi-annual, quarterly, monthly or daily compounding.
  • Instant compare: Toggle between Simple and Compound views to compare outcomes side-by-side.
  • Clear reset & reuse: Reset inputs quickly to run multiple scenarios without page reload.
  • Explainable formulas: Built-in explanations show the formulas used for both simple and compound interest.
  • Responsive & accessible UI: Mobile-first layout and keyboard-friendly controls for better usability.

Use Cases for Interest Calculator

  • Personal savings planning: Estimate how much your savings will grow over months or years using simple or compound interest.
  • Retirement projections: Model long-term compounding to compare different contribution amounts and frequencies for retirement goals.
  • Loan affordability: Quickly estimate interest owed on loans and compare simple vs compound scenarios to plan repayments.
  • Investment comparison: Compare returns across instruments (fixed deposits, recurring deposits, mutual funds) with different compounding frequencies.
  • EMI & amortization prep: Use the tool to validate monthly payment expectations and total interest for loan planning.
  • Short-term goal planning: Calculate how much you need to invest today to reach a specific amount in months or years.
  • Business cash-flow forecasting: Project interest on short-term business deposits or loans to manage working capital.
  • Education & milestone funding: Estimate growth required to fund education, travel, or major purchases by a target date.

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Interest Calculation Formula

Simple Interest
Interest = P × r × t
Total = P + Interest
  • P - Principal (initial amount).
  • r - Annual interest rate in decimal (e.g., 7.5% → 0.075).
  • t - Time in years. If you enter months, convert to years: months ÷ 12.
  • Example: P = ₹100,000, r = 0.09, t = 5 → Interest = 100000 × 0.09 × 5 = ₹45,000.
Compound Interest
A = P × (1 + r / n)^(n × t)
Interest = A − P
  • P - Principal (initial amount).
  • r - Annual nominal rate in decimal (rate% ÷ 100).
  • n - Compounding periods per year (annual = 1, semi‑annual = 2, quarterly = 4, monthly = 12, daily = 365).
  • t - Time in years (convert months to years by dividing by 12).
  • Example: P = ₹10,000, r = 0.075, n = 12, t = 2 → A = 10000 × (1 + 0.075/12)^(24) ≈ ₹11,570. Interest ≈ ₹1,570.

Notes: Inputs accept decimals. The UI converts months → years automatically for t. Displayed results are rounded for readability; calculations use full precision.

Interest Calculator FAQ

Simple interest is calculated only on the principal for the entire period (Interest = P × r × t). Compound interest is calculated on the principal plus any interest accrued in prior periods (A = P × (1 + r/n)^(n×t)), so compounding typically yields higher returns over time.

Use the Time field and choose the unit (Years or Months). When you choose Months the calculator converts months to years by dividing by 12 before applying formulas, ensuring consistent annual-rate calculations.

Compounding frequency (n) is how often interest is added to the principal per year (e.g., monthly = 12, quarterly = 4). More frequent compounding results in slightly higher returns for the same nominal annual rate.

Displayed results are rounded for readability, but underlying calculations use full floating-point precision to avoid cumulative rounding errors. Use the breakdown table for per-period values when available.

The calculator expects non‑negative values. Zero principal or zero time will yield zero interest. Negative inputs are not supported and may produce invalid results.

No. This tool provides estimates for planning and comparison only. It is not a substitute for official bank statements, tax guidance, or professional financial/legal advice.